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Wednesday, 10 June 2015

Construction of D.C. Generator

Construction of D.C. Generator Points : construction of d.c. generator, armature winding, field system, armature core, brushes, commutator D.C. generaiors and D.C. motors contain similar general construction. Indeed, as machine is being assemble; the workmen generally do not identify whether it is a d.c. generator or motor. A few d.c. generator can be run as a d.c. motcr and vice-versa. Every d.c. machines contain five principal components.
(i) Armature Winding
(ii) Field system
(iii) Armature Core
(iv) Brushes
(v) Commutator
(i) Armature Winding Slots of armature core hold insulate conductors that are attached in a proper method. This is identified as armature winding. This is winding in which “work” e.m.f. is induce. Armature conductors are attached in series- parallel; conductors being attached in series so as to enhance voltage and in parallel paths so as to amplify the current. Armature winding of a d.c. machine is a closed-circuit winding; conductors being attached in a regular manner forming a closed loop or series of closed loops. (iii) Armature Core Armature core is key to the machine shaft and rotate among field poles. It consists of slot soft-iron laminations (on 0.4 to 0.6 mm thick) that are stack to form a cylindrical core. Laminations are independently coated by a thin insulate film so that they do not arrive in electrical contact by all other. Function of laminating core is to decrease eddy current loss. Laminations are slot to hold and give mechanical security to armature winding and to give shorter air gap for flux to cross among pole face and armature “teeth”. (iv) Brushes Purpose of brushes is to make sure electrical connections among rotating commutator and stationary external load circuit. Brushes are prepared of carbon and rest on commutator. Brush pressure is used to by means of adjustable springs. If brush pressure is extremely large friction produces heating of commutator and brushes. On the other hand, if it is too frail, the flawed contact by commutator may generate sparking. (v) Commutator Commutator is mechanical rectifiers which convert alternating voltage generate in armature winding into direct voltage across brushes. Commutator is prepared of copper segment insulated as of each other by mica sheets and mount on shaft of machine. Armature conductors are soldered to commutator segments in a proper manner to provide rise to armature winding. Depending upon manners in which armature conductors are attached to commutator segments, there are two types of armature winding in a d.c. machine viz a. lap winding b. wave winding. Great care is taken in building commutator as any weirdness will cause brushes to bounce, producing unacceptable sparking. Sparks can burn brushes and overheat and carbonise the commutator.

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